In the related art, pressure sensors for measuring the pressure of fluid are widely used. The pressure sensors of this type include those used by being installed at a spot where the pressure of fluid containing corrosive chemical agents such as highly-refined nitric acid, hydrochloric acid, and hydrofluoric acid is measured as in a semiconductor manufacturing process, for example. More specifically, in a semiconductor manufacturing apparatus, chemical solution containing hydrofluoric acid or the like is used when performing an etching process on a semiconductor substrate, so that the pressure sensor is built in a circulation circuit for the chemical solution for ensuring stable supply of the chemical solution.
The pressure sensor of this type is provided at an end portion of a pressure introduction flow channel branched in a T-shape upward from a primary fluid flow channel in which fluid to be subjected to pressure measurement flows.
The pressure sensor as described above can be installed in pair in the primary fluid flow channel via an orifice and used as a flow meter which calculates the flow rate by converting the pressure difference between the both pressure sensors into the flow rate. Then, by controlling the flow rate calculated by the flow meter and the opening of a variable valve so as to eliminate the difference from the preset flow rate which is set in advance, a flow rate controller which performs a feedback control on the flow rate of the primary fluid flow channel to a desired value is achieved. (For example, see Patent Document 1).    Patent Document 1: Japanese Unexamined Patent Application Publication No. 5-233068 (see FIG. 1)